Layered network architecture is commonly used network architecture in telecommunication networks. At call setup a call control node (CCN) acts as media gateway controller (MGC). It selects a media gateway (MG) to switch the user plane and to provide in-band equipment if necessary. Possible call control nodes are for example MSC (Mobile Switching Center), GMSC (Gateway MCS), TSC (Transit Switching Center) or MGCF (Media Gateway Control Function). Possible in-band equipment is for example transcoder devices, echo canceller, or tone and announcement devices.
One call case in a circuit switched core network (CNCS) is an inter-MSC handover. This call case is described in 3GPP specification TS 23.009. In this call case a terminal is moving from a location area served from a CCN 1 to a location area served from a CCN 2. The control of the interface towards the radio access network (RAN) changes from CCN 1 and CCN 2. An interface for call control signaling has to be established between CCN 1 and CCN 2. If CCN 1 and CCN 2 control different MG then an interface for the user plane switching has to be established as well.
The need to hand over the control from one call control node (CCN1) to the other call control node (CCN2) may arise when a mobile terminal moves from an area covered by a UMTS network to another area which is covered by way of example by the GSM network. In FIG. 1 a network view from a mobile-related handover for the situation discussed above is shown. A call control node 10 which in the example shown is a mobile switching center MSC and which is also called “anchor MSC” provides a signaling interface towards the core network. The call control node 10 controls the first switching point which in the embodiment shown is a media gateway 15. A call should be handed over to another call control node, the non-anchor MSC 20, which provides the signaling interface towards the radio access network (RAN). The non-anchor MSC 20 controls a media gateway 25 which provides the user plane towards the radio access network. The interface between the MSC 10 and the MSC 20 is called E-interface signaling plane, whereas the interface between controlled media gateway nodes is called E-interface user plane.
In FIG. 2 the main steps of an inter-MSC handover procedure are shown which are relevant for the present invention:
At the start of inter-MSC handover the anchor MSC sends a prepare handover request (MAP) message to the non-anchor MSC (number 1 in FIG. 2).
At reception of this message in non-anchor MSC the non-anchor MSC prepares the radio resources for the target radio access (number 2 in FIG. 2). This includes the seizure of a RAN (Radio Access Network) termination in MG 2 (number 3 in FIG. 2).
Then non-anchor MSC gives control back to anchor MSC. Later anchor MSC sends a call control message over the E-interface to establish the E-interface user plane connection between the MG nodes controlled from anchor and non-anchor MSC. Depending on the applied call control protocol this can be a BICC IAM, ISUP IAM or SIP INVITE message (number 4 in FIG. 2).
Part of the establishment of the E-interface user plane connection the anchor and non-anchor MSC have to seize terminations in the media gateway nodes (number 5 and 6 in FIG. 2).
The termination on the core network side in anchor MSC is not modified during this process.
Currently the MAP prepare handover request includes no information about user plane resources seized in anchor MSC. Accordingly, non-anchor MSC has no information to optimize the media gateway selection when seizing the radio access network termination.